Existing cellular networks, such as (Global System for Mobile Communications (GSM) and IS95, are intended to provide contiguous and continuous coverage for cellular communication terminals, so as to support a high terminal mobility expected from such systems. However, despite careful network design, indoor (in-building) coverage, or the coverage of places with high shadowing attenuation (e.g. tunnels) of such networks is often “patchy”, with coverage “holes” at best, and no coverage at worst.
One main reason for the impaired indoor coverage is that cellular base stations are usually placed outside buildings, at positions that are typically higher than the average building heights, to provide large area coverage. Although the signal may be adequate at street-level, it is severely attenuated by a building's material as it passes through such buildings, reducing the signal power in-building, resulting in poor coverage. Loss of signal power (attenuation) depends on the building material and can be tens of decibels (dBs) for each wall penetration. The problem is exacerbated in third generation systems such as Wideband Code Division Multiple Access (WCDMA) and cdma2000, as these new systems have the capability of high data transmission, which results in lower information bit energy (Eb), and much reduced link budget and cellular footprint.
Typical solutions for providing indoor coverage are expensive and involve extensive investment in the cellular network infrastructure and are much more complex in planning and operation. One solution involves the use of a cellular repeater. Typically, repeaters operate in a manner that does not harm and/or effect the operations of the wireless communications network in which it operates. One of the fundamental tasks performed by a repeater for operating in such a manner is controlling the gain of the repeater. The repeater controls its gain to avoid increasing the interference levels in the wireless communications network. Typical repeater systems react to events in the wireless communications network much slower than the occurrence of those events, such as, for example, the start of a signal transmission in the uplink.
The output power level of a repeater is equal to the power at the input to the repeater plus the gain of the repeater. For example, if the repeater gain is 80 dB, and the input to the repeater is −80 dBm, the output power level of the repeater will be −80 dBm+80 dB=0 dBm. When the power at the input changes, the repeater will adjust its gain to either keep the power at output level, or to adjust the power at output to higher or lower, as necessary. If the input level to the repeater changes suddenly, typical repeaters do not have time to adjust their gain to achieve these outcomes.
Sudden changes in the power at input happen is when a handset initiates a call to the base station. During the initial part of this process called the Random Access phase, the handset will send out short bursts of information at ever increasing levels. The repeater's receiver gain needs to adjust to the changing input levels to ensure that the output signal for the repeater is not compromised by saturation of the input. After a large up-step in input signal power is detected, typical repeaters will increase their front-end gain in response to a drop in input signal power level to maintain the output signal power level.